1. Field of the Invention
The invention relates generally to the construction of electric motors, and more particularly to systems and methods for constructing electric motors in which powdered or particulate materials having high thermal conductivity and low electrical conductivity are introduced into the slots of a stator core to support the stator windings and conduct heat away from the windings.
2. Related Art
A typical electric motor has two primary components: a rotor; and a stator. The stator is a stationary component, while the rotor is a movable component which rotates with respect to the stator. In an AC induction motor, a magnetic field is induced into the rotor. The interaction of the magnetic fields created by the stator and the rotor cause the rotor to rotate with respect to the stator.
The motor incorporates electromagnets that generate changing magnetic fields when current supplied to the electromagnets is varied. These electromagnets are normally formed by positioning coils (windings) of insulated wire around ferromagnetic cores. In an AC induction motor, the ferromagnetic cores are formed between “slots” in the stator core. When electric current is passed through the wire, magnetic fields are generated around the wire and consequently in the ferromagnetic cores. Changing the magnitude and direction of the current changes the magnitude and polarity of the magnetic fields generated by the electromagnets.
Electric motors that are designed for downhole applications (such as driving an electric submersible pump) are typically AC induction motors. These motors, generally speaking, are long and narrow. Usually, downhole motors are less than 10 inches in diameter, and they may be tens of meters long. Although the motor can be manufactured in sections, the windings of the stator (or stator sections) are very long, and it may be difficult to keep the windings in place within the stator.
Conventionally, an encapsulant such as an epoxy, varnish or other thermoset material is introduced into the stator slots after the windings are installed. This encapsulant material serves to fill the void that in the slots that are not occupied by the windings, thereby holding the windings in position within the slots. The encapsulant also helps to conduct heat outward from the windings, thereby reducing the operating temperature of the motor. The encapsulant also helps prevent vibrations and rubbing of wires against each other which may result from vibrations.
Conventional encapsulants have a number of disadvantages. For example, the temperatures at which motors are operated in downhole environments are high enough in many applications that the encapsulants begin to break down and their desirable characteristics begin to degrade. Another problem is that conventional encapsulants undergo thermal expansion, so that changes in the temperature of the motor cause the encapsulant to expand and contract to a greater degree than is desirable. Yet another problem with the use of encapsulants in motors is that the encapsulants can hinder or prevent disassembly and repair/remanufacture of the motor, and the components which are in contact with the encapsulants (e.g., the stator laminatons) cannot be reused.
It would therefore be desirable to provide systems and methods for encapsulant-free manufacturing of stators for downhole motors.